Protein kinases are a group of enzymes for phosphorylation of hydroxyl groups in serine, threonine, and tyrosine moieties of protein. They are essential in growth factor signal transduction inducing cell growth, differentiation, and proliferation. Human protein kinases can be divided into tyrosine protein kinases and serine/threonine protein kinases. Tyrosine protein kinases can be further divided into receptor and cytoplasma/non-receptor kinases (Manning et al., Science, 2002, 298, 1912). Receptor tyrosine kinases possess cell surface domains to interact with growth factors, and cytoplasma domains to conduct phosphorylation of tyrosine moieties. As such, a growth factor can bind to the growth factors receptor site, thereby triggering polymerization of the receptor tyrosine kinase, and autophosphorylation of the tyrosine moieties in cytoplasma. Subsequently, sequential phosphorylation of subfamily proteins proceeds as signal transduction progresses, leading to overexpression of transcription factors and eventually cancer. A mutation or an overexpression of certain protein kinases may impact the signal transduction in a normal cell resulting in the imbalance of homeostasis in body. For example, continuous signal transduction may lead to cancer, inflammation, metabolic syndromes, and CNS diseases.
The bcr/abl fusion gene, formed by rearrangement of the breakpoint cluster region (bcr) on chromosome 22 with the c-abl proto-oncogene on chromosome 9, is present in CML (chronic myeloid leukemia) patients. The chromosome containing bcr/abl gene is referred to as Philadelphia chromosome (Nowell, J. Natl. Cancer Inst., 1960; 25:85). In the bcr/abl fusion gene, the bcr gene part contains oligomerization domains, and the abl gene part contains tyrosine domains. 3 principle forms (p190, p210 and p230 kDa) of bcr/abl gene, determined by the breakpoints of the bcr gene, have been reported. Gleevec (imatinib mesylate, STI-571) is the first targeted anti-cancer agent which was developed by Norvartis and released in 2002. Gleevec can selectively inhibit bcr/abl by inhibiting tyrosine kinases of abl. Gleevec is commonly used as standard treatment for CML. But acquired resistance to Gleevec became a serious problem. There are various mechanisms to cause the acquired Gleevec-resistance including amplification of bcr/abl gene, loss of bcr/abl gene, point mutations of bcr/abl gene. Among them, the most important factor inducing the acquired Gleevec-resistance is T315I-bcr/abl point mutation within the abl kinase domain. Multiple creative endeavors to overcome the acquired Gleevec-resistance were engaged. The recently released drugs such as Nilotinib and Dasatinib effectively inhibit many point-mutations of abl kinase domains generated by the acquired Gleevec-resistance. However, Nilotinib and Dasatinib are unable to inhibit T315I-bcr/abl mutant species. Therefore, there are a number of attempts to develop a medicine inhibiting T315I-bcr/abl mutation. Vascular endothelial growth factors (VEGFs) mediate a plethora of biological process in endothelial cells such as cell survival, proliferation, differentiation, angiogenesis, and migration. VEGFs are primarily produced by vascular endothelial, hematopoietic and stromal cells in response to hypoxia and upon stimulation of growth factors such as TGFs, PDGFs or interleukins. VEGFs bind to their high-affinity specific receptors VEGFRs (VEGFR-1, -2, and -3). Each VEGF isoform binds to a particular subset of these receptors leading to the formation of receptor homo- and heterodimers that activates discrete signaling pathways and executes its biological functions such as angiogenesis [Cébe-Suarez S, Zehnder-Fjällman A, Ballmer-Hofer K. Cell Mol Life Sci. 2006 March; 63(5): 601-15]. Angiogenesis provides tumors with nutrients, oxygen, and path for cancer cell spread. Therefore, it is essential for cancer cell proliferation and spread. Angiogenesis in normal body is balanced by co-regulation between angiogenic stimulators and angiogenic suppressors. However, in off-balanced cancer cells, VEGFR is activated by growth factors such as VEGF which have a great effect on vascular endothelial cells [Ann Hoeben, Bart Landuyt, Martin S. Highley, Hans Wildiers, Allan T. Van Oosterom and Ernst A. De Bruijn. Pharmacological Reviews. 2004 vol. 56(4): 549-580]. Various inhibitors (small synthetic molecules) of VEGF receptor tyrosine kinases are being developed, most of which are able to be used in solid tumors and to inhibit angiogenesis activated only in cancer cells and have a tremendous medicinal action with fairly low side effects.